RNA interference (RNAi) refers to a phenomenon where a double stranded RNA consisting of a sense RNA having a homologous sequence with the mRNA of a target gene and an antisense RNA having a complementary sequence therewith is introduced to cells to selectively induce the degradation of the target gene mRNA or suppress the expression of the target gene. The RNAi was first found in nematodes and for now, it is observed in various organisms including yeasts, insects, plants, humans, as a highly preserved biological phenomenon.
A small interference RNA (siRNA), as a material of inducing RNAi, refers to a short double helical strand consisting of about 20 to 30 nucleotides. The introduction of an siRNA into cells enables to target mRNA of which the base sequence is complementary to the siRNA, thereby suppressing the expression of its gene. Hence, the siRNA has been paid much attention as an efficient means capable of controlling a life process to be a target by virtue of its therapeutic effects against diseases, and easy preparation and high target selectivity thereof.
Currently, cancers, virus infection diseases, autoimmune diseases, and neurodegenerative diseases have been studied as diseases to be curable by use of siRNAs, and their potentials as therapeutic agents for age-related macular degeneration (Bevasiranib; Opko Health, Inc., Miami, Fla., USA; clinical phase III) and respiratory syncytial virus infection (ALN-RSV01; Alnylam, Cambridge, Mass., USA; clinical phase II) have been reported as clinical trials thereof. Furthermore, it was reported that the delivery system of siRNAs in human cancer therapy is possible by using cyclodextrine-based nano particle polymers having transferrin as their target (Oh Y K. et al., Adv Drug Deliver Rev 2009, 61, 850-862).
However, the siRNAs are in vivo degraded within a short time due to their low stability and the anionic nature thereof hinders them from readily penetrating cell membranes with the same negative charge, leading to low transmissibility into cells and thus, there is a demand on efficient delivery vehicle technology capable of making their intracellular delivery easy. Accordingly, in order to efficiently deliver siRNAs into cells, there is needed an effective novel delivery system capable of having resistance against degradation enzymes, circulating in living body for a long time and reaching target cells via a clinically available injection route, and enabling an effective cytoplasm release after the cell penetration thereof.
As existing siRNA delivery vehicles, recombinant plasmids or virus vectors of expressing siRNA were used, or lipofectin, lipofectamine, cellfectin, cationic phospholipid nanoparticle, cationic polymer, or liposome-based delivery vehicles were usually used. However, viral delivery vehicles are restricted by the size of a gene to be delivered and they do not guarantee in vivo stability thereof because they might cause immune side effects due to the immunogenicity of the surface proteins of the virus vectors. Further, the delivery vehicles using cationic molecules or synthetic polymers have showed low transport efficiency into cells and had cell toxicity problems which might result from gene delivery procedures into cells.